1. Field of the Invention
This invention relates to a method and an apparatus for laser scribing of coated layers on glass sheet substrates.
2. Background Art
Laser scribing of coated layers on glass sheet substrates has been done for many years as disclosed by U.S. Pat. No. 4,292,092 Hanak. To a large extent, the laser scribing is performed by a laser beam that is directed from the coated side of the substrate; however, the scribing has also been performed by directing the laser beam through the glass sheet substrate to the coated layers to be scribed such as disclosed by U.S. Pat. No. 4,568,409 Caplan, U.S. Pat. No. 4,854,974 Carlson et al., U.S. Pat. No. 4,892,592 Dickson et al., U.S. Pat. No. 5,296,674 Praschek et al., and U.S. Pat. No. 5,593,901 Oswald et al.
Traditional laser processing systems are of two types. One type includes a fixed laser head mounted over a movable XY table (two axis) on which the coated glass sheet is supported for the scribing, while the other type includes a single axis movable laser scanning head mounted over a single axis movable table. The major drawback of the first type is the speed limitation of large XY tables, which is generally in the range of about 300 to 500 millimeters per second. Thus, in order to achieve commercially practical output, it is necessary to use multiple lasers or split beams to feed several laser nozzles. In addition to being expensive, such systems require maintaining optical alignment which is difficult and also require that the power to each nozzle be independently controlled. In addition, it is imperative to have real time spacing and adjustment between nozzles to facilitate the spacing between scribes. The other system also has the same problems since it is difficult to move the laser head faster than about 700 to 800 millimeters per second.
Other laser scribing patents noted during an investigation conducted in connection with the present application include U.S. Pat. No. 4,603,470 Yamazaki, U.S. Pat. No. 4,689,874 Nishiura, and U.S. Pat. No. 5,956,572 Kidoguchi et al.
An object of the present invention is to provide an improved method for laser scribing glass sheet substrate coatings at a relatively high speed so as to thereby provide a cost effective product.
In carrying out the above object, the method for laser scribing is performed with a glass sheet substrate having oppositely facing surfaces one of which is uncoated and the other of which is coated. The coated substrate is conveyed along a direction of conveyance adjacent a laser source that provides a pulsed laser beam with a wavelength at a near-infrared fundamental frequency and having a pulse frequency in the range of 50 to 100 kilohertz and a pulse duration in the range of 8 to 70 nanoseconds. The pulsed laser beam is reflected from the laser source by an XYZ galvanometer controlled mirror system toward the uncoated surface of the glass sheet substrate for passage therethrough to the coating on the other surface to provide overlapping ablations through the coating and scribing thereof at a speed of at least 1000 millimeters per second.
The glass sheet substrate is conveyed in a vertical orientation and is positioned laterally with respect to the direction of conveyance by gas pressure and vacuum positioners located upstream and downstream along the direction of conveyance from the location at which the pulsed laser beam passes through the substrate such that the positioners control the planarity of the substrate. The gas pressure and vacuum positioners position the glass sheet substrate at its uncoated surface so there is no degradation of the coated surface.
Laser detectors detect the exact position of the coated substrate so the scribing laser beam can be properly focused.
In one practice of the method, the conveyance of the coated glass sheet substrate is provided by indexing thereof with the substrate being held stationary during the laser scribing.
In another practice of the method, the laser scribing is performed as the coated glass sheet substrate is conveyed.
In performing the laser scribing method, the coated glass sheet substrate is disclosed as having a plurality of different coated layers and a plurality of the laser scribes are made at different power levels so the scribes extend through different layers. More specifically, in the most rapid performance of the laser scribing method, a plurality of laser sources and associated XYZ galvanometer controlled mirror systems respectively provide the pulsed laser scribing of the different scribes at different power levels, each with a wavelength at a near-infrared fundamental frequency and with pulse frequencies in the range of 50 to 100 kilohertz and pulse durations in the range of 8 to 70 nanoseconds and at scribing speeds of at least 1000 millimeters per second.
Another object of the present invention is to provide improved apparatus for laser scribing a coating on a glass sheet substrate.
In carrying out the immediately preceding object, the apparatus of the invention includes a conveyor for conveying a glass sheet substrate along a direction of conveyance with the substrate having oppositely facing surfaces one of which is uncoated and the other of which has a coating. A laser source provides a pulsed laser beam with a wavelength at a near-infrared fundamental frequency and having a pulse frequency in the range of 50 to 100 kilohertz and a pulse duration in the range of 8 to 70 nanoseconds. An XYZ galvanometer controlled mirror system reflects the pulsed laser beam from the laser source toward the uncoated surface of the glass sheet substrate for passage therethrough to the coating on the other surface to provide overlapping ablations through the coating and scribing thereof at a speed of at least 1000 millimeters per second.
The apparatus supports the substrate in a vertical orientation and includes gas pressure and vacuum positioners located upstream and downstream along the direction of conveyance from the location at which the pulsed laser beam passes through the substrate such that the positioners control the planarity of the substrate during the laser scribing.
The apparatus includes laser detectors that detect the exact position of the coated substrate so the scribing laser beam can be properly focused.
The apparatus disclosed includes a plurality of the pulsed laser sources that operate at different power levels, each with a wavelength at a near-infrared fundamental frequency and with a pulse frequency in the range of 50 to 100 kilohertz and a pulse duration in the range of 8 to 70 nanoseconds, and a plurality of XYZ galvanometer controlled laser mirror systems of the apparatus respectively reflect the pulsed laser beams from the laser sources to provide scribing at speeds of at least 1000 millimeters per second.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.